Factors Affecting the Intelligibility of Low-pass Filtered Speech

Frequency compression is an effective alternative to conventional hearing aids amplification for patients with severe-to-profound middle- and high-frequency hearing loss and with some low-frequency residual hearing. In order to develop novel frequency compression strategy, it is important to first understand the mechanism for recognizing low-pass filtered speech, which simulates high-frequency hearing loss. The present work investigated three factors affecting the intelligibility of low-pass filtered speech, i.e., vowels, temporal fine-structure, and fundamental frequency (F0) contour. Mandarin sentences were processed to generate three types (i.e., vowel-only, fine-structure-only, and F0-contour-flattened) of low-pass filtered stimuli. Listening experiments with normal-hearing listeners showed that among the three factors assessed, the vowel-only low-pass filtered speech was the most intelligible, which was followed by the fine structure-based low-pass filtered speech. Flattening F0-contour significantly deteriorated the intelligibility of low-pass filtered speech.